Helicoptor Design: Advancing Blade Concept (ABC)
nove...@agate.net
Helicoptor Design: Advancing Blade Concept (ABC) Post (Part II)
Hello,
I am just a student who has an interest in helicopters and helicopter
design. From reading various books and searching the net I have
compiled a short list, based on my understanding, of
advantages/disavantages of ABC helos as you can see below. I'm always
searching for more information on this topic, so if you can help
please do so. Helo pilots/engineers please correct or add any
comments as you see fit. Thank you.
--
Advantages & Disadvantages of Advancing Blade Concept* (in comparison
to standard helicopter designs)
Advantages:
Contra-rotating main rotors cancel out each other’s torque,
eliminating the need for a tail rotor.
Elimination of tail rotor allows for a simpler, more compact fuselage
design.
Elimination of tail rotor makes the helicopter quieter.
Elimination of translation tendency (tendency for a helo to drift
sideways during a hover because of the tail rotor).
Elimination of tail rotor allows virtually all engine power to be used
to produce lift, thus making the craft more efficient (tail rotors may
rob up to 30% of total engine power, and they don’t use any of that
power for lift).
Asymmetry of lift during horizontal motion is eliminated, and thus
retreating blade stall as well.
Helicopter’s top speed may be increased because of the elimination of
the retreating blade stall danger.
Contra-rotating blades cancel out the vortexes created by each blade
and thus conserving power and increasing thrust.
(Arguable) ABC design is safer because it eliminates the possibility
of a tail rotor failure, which would obviously be disastrous on a
standard helicopter.
Disadvantages:
Requires more complex and heavier gearboxes and swashplates.
More expensive to design/develop.
(Arguable) Increased maintenance and repair difficulties.
?
* Advanced Blade Concept (ABC) as pioneered by the Sikorsky S-69
project. Utilizes two 3-bladed coaxial, contra-rotating rotors. Very
rigid blades allow the two rotors to be placed very close to each
other. Contra-rotating main rotor design eliminates the need for a
tail rotor, thus negating associated aerodynamic and control
complexities while increasing power efficiency and permitting the
helicopter to travel at much higher speeds.
Questions:
1. Since an ABC helicopter would have two sets of rotors dedicated
for lifting thrust, would this mean that the rotors would not have to
spin as fast to create the required lift for flight/hover as those of
a standard, single main-rotor helo? Would this make the helicopter
even quieter, given that it does not have a tail rotor either?
2. Are there any coaxial, contra-rotating helicopters with more than
three blades to each rotor?
3. Is yaw control sacrificed at all in an ABC helo?
4. Why was the Advancing Blade Concept not pursued further?
5. Is control/movement of a rigid-rotor system any different than a
standard, articulated rotor design and how so?
--
-JK
Free DVD! Fight DIVX!
Erich Freymann
nove...@agate.net wrote:
> (Arguable) ABC design is safer because it eliminates the possibility
> of a tail rotor failure, which would obviously be disastrous on a
> standard helicopter.
Arguable in deed. If the tail rotor should fail on a normal
helicopter, the pilot procedure is to disengage the engine,
or shut down if necessary. This would lead to an auto-
rotational descent to a safe landing, provided the flight
regime allows entry into auto-rotation.
> (Arguable) Increased maintenance and repair difficulties.
As an aircraft mechanic, I can safely say it will increase
maintenance and repairs. The tail rotor on normal helis is
simple compared to the main rotor system. These birds have
twice the main rotor instead of the tail rotor...
> Questions:
>
> 1. Since an ABC helicopter would have two sets of rotors dedicated
> for lifting thrust, would this mean that the rotors would not have to
> spin as fast to create the required lift for flight/hover as those of
> a standard, single main-rotor helo? Would this make the helicopter
> even quieter, given that it does not have a tail rotor either?
I would assume this with a possible combination of smaller-spanned
blades.
Such is the same when using a four or five blade main rotor rather
than a two blade rotor. Each blade is shorter on the multi-blade
rotor. Given that a shorter blade equates to a slower tip speed,
noise should be reduced as well.
>
> 3. Is yaw control sacrificed at all in an ABC helo?
Not at all. Yaw control is similar to that of the Kamov Hormone,
differential collectives allow differential yawing moments
between the two rotors. This allows total yaw control. Also,
an aerodynamic rudder control surface is used in conjunction
to allow greater yaw control in forward flight.
>
> 4. Why was the Advancing Blade Concept not pursued further?
Money. Not much demand for such a machine. The typical heli
orientation works so well, and is so versatile, it is not
cost effective to create such a specialized machine. Keep
in mind that ABC machines' main purpose was to break the
speed restrictions of the advancing blade problem. With
the production of the Osprey, and now a commercial vatiant,
this technology is again on the back burner.
>
> 5. Is control/movement of a rigid-rotor system any different than a
> standard, articulated rotor design and how so?
This uaually involves the use of elasto-meric components that flex,
twist, and bend. No mechanical hinges are needed or used with such
components. The use of composites has shown to be very reliable and
maintenance free (Aerospatial AS-350 has an elasto-meric hub...no
bearings.)
Hope this helps a bit....
Erich Freymann
Resume excluded for brevity
Seven7ths
>Asymmetry of lift during horizontal motion is eliminated, and thus
>retreating blade stall as well.
>
>Helicopter’s top speed may be increased because of the elimination of
>the retreating blade stall danger.
I'm no physicist, but my thoughts are:
Overall lift may be symmetrical, but each rotor disk individually will
experience retreating blade stall and lift dissymmetry. This may cause the
disks to crash into each other as they tilt in opposite directions.
jlb...@ibm.net
I can partially answer some of your questions. First, note that a tail
rotor failure is not "obviously disastrous". I have flown and landed single
main rotor helicopters with failed tail rotor. I know of others which have
been successfully flown and landed with the entire tail rotor and gearbox
gone. Not all such helicopters are so tolerant of a loss of tail rotor
thrust, however.
The Kamov design bureau in Russia builds counterrotating rotor helicopters
with more than three blades per set. Theirs are set farther apart than
those of the ABC ship. The controls for the rotors are different from and
arguably more complex than those of more conventional rotor systems when you
are looking at the moving controls and static linkages. The controls that
the pilot puts his hands on look the same and work (for the pilot) the same
as for more conventional helicopters. Even for conventional single main
rotor helicopters, the setup on the linkages is amazing, and can only be the
product of both brilliant engineering and a very warped mind.
David Lednicer
I worked on the ABC late in its life, reducing flight test and wind
tunnel data and simulating it in the aero group's codes.
The ABC had a lot of advantages. It had a higher hover Figure of Merit
than the average helicopter, due to its co-axial arrangement. With the
J-60s installed, it had the ability to accelerate from hover without
changing body attitude, which helped in combat tasks. By changing the
phasing of the two rotors slightly, rotor-induced vibration could be
controlled. The counter rotating rotors balanced out the moments
resulting from retreating blade stall and eliminated the need for a tail
rotor. Lastly, it was fast and manouverable. The manouverability came
from the high effective hinge offset of the rigid rotors.
The downsides were that it sucked fuel like a pig, primarily due to the
J-60s, which weren't intended for flying on a slow helicopter (compared
to a business jet). It was difficult to use the ABC arrangement for
anything but an attack helicopter, due to the big, tall gearbox
assembly. The rotors had to be well separated and very stiff so that
they wouldn't strike at high blade deflections. This resulted in a tall
mast, which was very draggy. Inter-rotor fairings were designed and
wind tunnel tested, but it was difficult to design a fairing that really
resulted in a drag decrease. Initially, there were problems with
control, which led to the crash of the first prototype, but these were
later fixed.
There was a proposal for a XH-59B follow-on, which would have had a
ducted prop replacing the two J-60 jet engines. The PT6s would have
powered the rotor in hover and the prop in high speed cruise.
Unfortunately, the project didn't go ahead. The tilt-rotor killed the
ABC concept.
> Questions:
>
> 1. Since an ABC helicopter would have two sets of rotors dedicated
> for lifting thrust, would this mean that the rotors would not have to
> spin as fast to create the required lift for flight/hover as those of
> a standard, single main-rotor helo? Would this make the helicopter
> even quieter, given that it does not have a tail rotor either?
The tip speed on the S-69's rotors was a little lower than the average
Sikorsky helicopter. It was a little quieter than a S-76, due to the
lack of a tail rotor, but the aux propulsion J-60s were VERY noisy.
> 2. Are there any coaxial, contra-rotating helicopters with more than
> three blades to each rotor?
I have seen coaxials with two bladed rotors, but this isn't common. A
note: a coaxial is not necessarily an ABC. Kamov helicopters are not
ABCs.
> 3. Is yaw control sacrificed at all in an ABC helo?
No, not at all. If I remember right, in hover, yaw control is achieved
by differential collective and in high speed forward flight, there were
rudders.
> 4. Why was the Advancing Blade Concept not pursued further?
The US Army decided they didn't want it. The tilt rotor helped bring
about its demise.
> 5. Is control/movement of a rigid-rotor system any different than a
> standard, articulated rotor design and how so?
No.
-------------------------------------------------------------------
David Lednicer | "Applied Computational Fluid Dynamics"
Analytical Methods, Inc. | email: da...@amiwest.com
2133 152nd Ave NE | tel: (206) 643-9090
Redmond, WA 98052 USA | fax: (206) 746-1299
vic
Erich Freymann wrote:
>
> Arguable in deed. If the tail rotor should fail on a normal
> helicopter, the pilot procedure is to disengage the engine,
> or shut down if necessary. This would lead to an auto-
> rotational descent to a safe landing, provided the flight
> regime allows entry into auto-rotation.
>
Perhaps the poster wasn't clear about the type of failure, no power to
the tail rotor, fixed pitch, loss of components???
--
"I do not require that a helicopter have more than one engine, but
I do require that it not have more than one main rotor." -vic
Dennis McGuire
One of the features of the ABC design was extremely stiff blades
(titanium spars) with no flap hings.
Maury Markowitz
In <350822...@amiwest.com> David Lednicer wrote:
> rotor. Lastly, it was fast and manouverable. The manouverability came
> from the high effective hinge offset of the rigid rotors.
How so, because it was effectively doubled?
> There was a proposal for a XH-59B follow-on, which would have had a
> ducted prop replacing the two J-60 jet engines.
Whoa, the J-60 was for FORWARD THRUST?!? How fast could this thing go?
> I have seen coaxials with two bladed rotors, but this isn't common. A
> note: a coaxial is not necessarily an ABC. Kamov helicopters are not
> ABCs.
Ok, what is the difference (if you don't mind me asking).
> The US Army decided they didn't want it. The tilt rotor helped bring
> about its demise.
Odd in retrospect, considering it still hasn't _really_ gone anywhere. Oh
well.
Maury
Maury Markowitz
In <CDWN.48$yg1.2...@ptah.visi.com> Chris Johnson wrote:
> It seems like one possibility to keep the blades from colliding is to
> arrange their positions so that no 2 blades are aligned vertically.
> But that requires a static relationship between the 2 rotors. Is
> this the case, or are the 2 rotors allowed to vary RPM independently
> in existing designs? If they can vary, what's the reason or design
> need which drives this?
I was thinking about that too. Then I thought "oh, they're going in
opposite directions".
Maury
Agcatman
>OK, let's here from the CFIs out there, autorotation vs running landing?<BR
If I've got power, I'm using it. In a running landing situation, providing
that control can be maintained, it would be possible to abort if necessary.
Just increase forward speed gently, and go around and do it right. If you
choose to auto, and there's a problem at the bottom, that's too damn bad.
You're committed. Try pulling power to get out of that, and you're going to
ride the Merry-Go-Round, and it ain't gonna be much fun.
Now I'm not familiar with the flying characteristics of too many helicopters
that have lost their tail rotor systems, but some are unflyable. The loss of
the tail rotor completely throws the center of gravity out of whack. But in
that case all you can do is say your prayers and hope for the best. But if
the aircraft is flyable, and you have power, use it. Screw the autos. If you
know what you are doing you can make a nicer landing with power and a hell of a
lot less risk.
Stephen Austin
Austin Ag Aviation
Comm. Rotorcraft/Helicopter, CFI and CFII Helicopter
Comm. SEL and MEL
Instrument Airplane and Helicopter
vic
Chris Johnson wrote:
_snip_
> It seems like one possibility to keep the blades from colliding is to
> arrange their positions so that no 2 blades are aligned vertically.
> But that requires a static relationship between the 2 rotors. Is
> this the case, or are the 2 rotors allowed to vary RPM independently
> in existing designs? If they can vary, what's the reason or design
> need which drives this?
What am I missing here? On the ABC aircraft you have two rotors, one
above the other, turning in opposite directions so that you always have
advancing blades on both sides of the rotor disk. How could you
"arrange their positions so that no 2 blades are aligned vertically"?
Every blade on the upper rotor will be aligned vertically with every
blade on the lower rotor twice during every revolution.
Agcatman
>>OK, let's here from the CFIs out there, autorotation vs running landing?<BR>
Well, I'll try it again seeing how my last post got eaten somewhere.
A running landing would be my choice any day of the week over an auto. Doing a
running landing, if the helicopter is controllable, is your best option because
it allows you to make a mistake. If you see you're going to overshoot, or
whatever, it is a relatively simple matter to *gently* pull a little power and
go around to do it again. If you commit yourself to an auto, that's all she
wrote. There's no pulling power at the bottom of that, unless you like
spinning like mad before you crash. Now I'm not saying that you couldn't do an
auto, I'm just saying that if I have power, I'm gonna use it. Now this is all
assuming that the aircraft is controllable. In some aircraft, if you lose the
tail rotor assembly, (like it falls off due to vibration), you are going nose
first into the ground, and auto or running landing is the least of your
worries. That tail rotor back there creates a heck of a moment, and if you
lose it, you've lost the C of G. That's real bad. But that doesn't happen
very often. Anyway, to reiterate, in my opinion, if you have power, use it.
Screw the auto. Save that for the engine failures or the tail rotor failures in
a hover.
Jeff McCullars
I've had a loss of tail rotor control before in a UH-1. Your correct it's
not much fun. During night flight we were at the point of transition from
approach to hover when the nose started to spin slowly to the right. It
accelerated quickly for about 25 turns. The thing I noticed first was that
it did not spin in a level attitude. It was left wing and nose down (in a
counter-clockwise rotor system). Centered on the left seat chin bubble.
The Emergency procedure is to roll off the throttle which will level the
aircraft and stop the spin. I had no safe place to land and so eventually
attained some forward airspeed. In flight the aircraft trimmed nicely and I
was able to make a power on running landing. Using engine torque to stay on
the runway.
If the aircraft is controllable don't auto right away. Take time to see how
she handles. One option may be to fly to the runway, make a trimmed
approach, then auto if it gets out of control. The decision to make an auto
over a running landing should come before you pass the 90 degree mark in the
spin (in flight). Once you've passed this point you may not be able to
recover even if you do auto. Every helicopter I've flown will fly without a
working tail rotor as long as it stays attached to the aircraft. You'll
have to find the airspeed/power balance point though.
One last thing. It's not all over just because your on the ground. If your
screeming down the runway at 90 kts how will you stay on the runway? If you
catch a skid/wheel and roll over it will not be a very pretty sight. You
might use enging torque to turn the nose or for/aft cyclic will help a minor
amount. Wheel brakes are great for this sort of emergency.
Jeff McCullars
USCG
Instructor Pilot/Instrument flight examiner/Night Vision Goggle instructor
4500TT TH-55, UH-1, UH-60A, Bell 206, AS-355, BO-105, HH-3F, H-60J
je...@eagle.ptialaska.net
Agcatman wrote in message <19980312230...@ladder01.news.aol.com>...
>>OK, let's here from the CFIs out there, autorotation vs running
landing?<BR
>
>If I've got power, I'm using it. In a running landing situation,
providing
>that control can be maintained, it would be possible to abort if necessary.
>Just increase forward speed gently, and go around and do it right. If you
>choose to auto, and there's a problem at the bottom, that's too damn bad.
>You're committed. Try pulling power to get out of that, and you're going
to
>ride the Merry-Go-Round, and it ain't gonna be much fun.
>
>Now I'm not familiar with the flying characteristics of too many
helicopters
>that have lost their tail rotor systems, but some are unflyable. The loss
of
>the tail rotor completely throws the center of gravity out of whack. But
in
>that case all you can do is say your prayers and hope for the best. But
if
>the aircraft is flyable, and you have power, use it. Screw the autos. If
you
>know what you are doing you can make a nicer landing with power and a hell
of a
>lot less risk.
>
>
nove...@agate.net
I'm glad I've gotten some responses from my original post... more info
is always a help. Unfortunately, it seems that my news server has
missed some of the posts in this thread (i.e. Chris Johnson's &
others?) and so I can only see segments of them in other replies.
Please Email as well as post responces if you want to be sure I get
it... :\
As far as I can tell, the major negative point for ABC that I am
hearing of is the serious danger of rotor blade collision. I don't
know, but the ABC idea still sounds too good to be forgotten about.
So many of the control & aerodynamic oddities of Main&tail-rotor
helicopters (and NOTAR helos as well) are eliminated with ABC, that I
think it would be worthwhile to try to work out current
difficulties... but that's just an opinion of a non-expert.
Here is some specific stuff I have read about regarding this topic:
"Another promising idea was the ABC (advancing blade concept). [brief
discription]... No matter what loads might be encountered, the blades
*could not* collide with each other. There was nothing terribly
complex with the idea, which promised to overcome the basic difficulty
that stands in the way of a fast helicopter... The Sikorsky S-69, in
a programme funded mainly by the US Army, flew successfully at 316mph
(509km/h). No insuperable problems were encountered, *and it appears
surprising that nothing has been done to take this promising idea
further*..."
This is taken from Combat Arms: Modern Helicopters... a really cheap
hobbiest book, but it was written by a guy from Jane's (Bill Gunston).
Another question: Just how hard & expensive is it to make rotor
blades rigid enough to be suitable for ABC, relatively speaking?
Matthew Saroff (Remove .123456 to reply)
mal...@concentric.net (Sean Malloy) wrote:
>nove...@agate.net wrote:
>>Helicoptor Design: Advancing Blade Concept (ABC) Post (Part II)
>
>>4. Why was the Advancing Blade Concept not pursued further?
>
>A number of nasty problems dealing with the design, which limit
>performance. The ugliest one is blade collision. When a rotor spins,
>it is distorted by the lift it generates from a flat disk into a cone,
>whose angle is determined by the rigidity of the hub mount, the
>rigidity of the blades, and the RPM/angle of attack of the blades.
>When you move this rotor disk through the air, the advancing blades
>produce more lift and the retreating blades product less; this tilts
>the cone toward the retreating side. If you put a _second_ rotor
>coaxial with the first, but rotating the other way, its retreating
>blades will be over the lower rotor's advancing blades -- the
>high-side blades of the bottom rotor bending up toward the low-side
>blades of the upper rotor. This produces a limit to a) the amount of
Hi,
Your description misses one of the fundamental principles
of the advancing blade concept. The retreating blade is off
loaded, which eliminates many of the problems of retreating blade
stall and blade flex.
That being said, the transmissions necessary for coaxial
rotors or props are hairy to design and maintain, which is one
reason why tail rotors (and now NOTAR) seem to be favored.
The Kamov coaxial designs were designed in response to
naval needs, and helicopters without tail rotors are typically
shorter and require less hangar space on shipboard.
The Kaman intermeshing rotor designs have the same
advantage, with less mechanical complexity, but less aerodynamic
efficiency.
--
Matthew Saroff | Standard Disclaimer: Not only do I speak for
_____ | No one else, I don't even Speak for me. All my
/ o o \ | personalities and the spirits that I channel
______|_____|_____| disavow all knowledge of my activities. ;-)
uuu U uuu |
| In fact, all my personalities and channeled spirits
Saroff wuz here | hate my guts. (Well, maybe with garlic & butter...)
For law enforcment officials monitoring the net: abortion, marijuana, cocaine,
cia,plutonium, ammonium nitrate, militia, dea, nsa, pgp, hacker, assassinate.
Send suggestions for new and interesting words to:
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Check http://www.pobox.com/~msaroff, including The Bad Hair Web Page
Agcatman
>I'm not a CFI, but I have flown a fair number of types, for over<BR>
>10,000 hrs, & IMHO it depends entirely on the helicopter, the degree<BR>
>of failure, where you are, & what the operator's manual says.<BR>
><BR>
>In other words, there is no one correct answer.<BR>
><BR>
>-- <BR>
>Regards,<BR>
><BR>
>Stan<BR>
></HTML>
Stan,
You are correct. I was probably a little quick in answering what can be a very
complex subject. I should have been a little more careful in the way I worded
my answer. But, in all the different models I've ever instructed in, not one
of their operator's manuals has ever advocated autorotation because of a tail
rotor failure at altitude. Now I'll also be quick to tell you that by no means
have I flown or instructed in them all, so there is a lot of room for others to
comment. I do have a pretty fair amount of experience in different types
though.
And I'd still stand by my answer, as a "rule of thumb" if nothing else. If the
aircraft is flying don't autorotate. Even if you only have partial power,
that is better than nothing as long as it is sufficient for you to maintain
rotor RPM. Anytime you can make a running landing, as opposed to an
autorotation, you're going to be better off. There are a lot of variables to
take into account, but I can't think of a single situation where an auto is
better than a running landing if RPM is maintainable. An autorotation is
always a possiblity if things suddenly get worse, but why limit yourself to
that option if there are other possibilities? In other words, leave yourself
an out. If you have to take it, then it's there. But by entering
autorotation, you have just taken away all your other options, and you are
stuck with it, come heck or high water. That's why it's important to keep the
speed up when doing a running landing. That way you're out of deadman's curve,
and the autorotation is still in your bag of tricks if the audience is getting
bored. :^)
Jonathan Johnson
>nove...@agate.net wrote in message <3508913c...@news.agate.net>...
>
>Here is some specific stuff I have read about regarding this topic:
>"Another promising idea was the ABC (advancing blade concept). [brief
>discription]... No matter what loads might be encountered, the blades
>*could not* collide with each other.
Not that I know much about the Ka-50 Hokum, but the idea of designing a
helicopter with two counter-rotating blades stacked on top of each other
seems ingenious. It seems almost impossible that the blades could collide
without first fracturing the mast at least, which by then you're screwed
anyway.
Earlier someone here mentioned that removing the tail rotor system from a
design would allow for all power to be used on the main rotor system, thus
providing a more efficient lift system. This would seem true and especially
reflects in the top speed of the Hokum being 350 km/h (219 mph / 190 kts).
Any opposing viewpoints?
>that stands in the way of a fast helicopter... The Sikorsky S-69, in
>a programme funded mainly by the US Army, flew successfully at 316mph
>(509km/h). No insuperable problems were encountered, *and it appears
>surprising that nothing has been done to take this promising idea
>further*..."
Look at the Lockheed AH-56 Cheyenne (which is now unfortunately decaying in
front of Ft. Rucker's Army Aviation Museum) which was supposed to be the
predecessor to the AH-64 and could reach speeds up to 410 km/h (256 mph /
222 kts), but from what I understand had problems with retreating blade
stall that where never worked out.
--
"Got my knees in the breeze and my ass in the trees!"
- A description of NOE flight
"Blessed be the Lord my strength, which teacheth my fingers to fight and my
hands to war." - Gen. Robert E. Lee, 1863
**** Remove NOSPAM from address to email author ****
vic
We were told at the time that the reason for scrapping the AH-56 was
that the cost of the black boxes and modules got out of hand. There was
little problem with retreating blade stall since the rotor unloaded at
speed due to the stub wings.
.
The design had almost every possible component configured as part of a
box or module. If the ship had a maintenance problem it could be
corrected in minutes. The mechanic was to go up to the ship, plug in a
computer (like your auto repair shop does now), and the computer would
indicate which box/module to replace. The ship was quickly back in
service and a shop mechanic or rear element logistics activity
fixed/replaced the box. The cost of the boxes that had to be on shelves
and in the logistics pipeline was too overwhelming.
.
There could have been other reasons but this was "the" story and we were
good soldiers and believed "them".
.
Question: Why did we pay more to cancel the Heavy Lift Helicopter (HLH)
project than it would have cost to complete a flyable ship? It would
have been of some research value. Oh well. Another possibility lost for
reasons best known by "them". -vic
.
David Lednicer
Maury Markowitz wrote:
> How so, because it was effectively doubled?
The further out the flapping hinge is, the higher the head moment and
the higher the control power. Trouble is, it is hard to put a
mechanical flapping hinge further out than a couple of percent (the
Brantly-Hynes helicopters being an exception to this). With a "rigid"
rotor, such as on the Bo 105, you get rather high effective flapping
hinges and high manouverability. We had a video at Sikorsky of a Bo 105
doing a full aerobatic routine, including manouvers impossible to do in
an airplane.
> Whoa, the J-60 was for FORWARD THRUST?!? How fast could this thing > go?
Yup, two J-60s urging it forward to up to 238 knots in level flight
(according to an old fact sheet I have). Thats 274 mph for you
landlubbers. Without the J-60s, it was capable of about 160 knots in
level flight. The difference is that without the J-60s, the rotors had
to provide the forward thrust.
> Ok, what is the difference (if you don't mind me asking).
Co-axials, like the Kamovs have mechanical hinges with low offset. To
avoid rotor-rotor contact, they are well separated vertically. The ABC
has very, very rigid blades that don't need excessive vertical
separation.
In high speed forward flight, the retreating blade stalls on a
helicopter. On the ABC this is no big deal and the two rotors cancel
out each other's moments. On a co-axial, each rotor is trimmed to have
no moment. Hence retreating blade stall is a limiting factor on top
speed for a co-axial.
> Odd in retrospect, considering it still hasn't _really_ gone
> anywhere.
True, but remember - Sikorsky initially pitched the ABC against the
tilt rotor for JVX. In the end, the DoD specified that the JVX had to
be a tilt rotor. Additionally, the ABC was pitched for LHX (admittedly
a better mission for it) and Bell initially pitched a tilt rotor.
Eventually, the US Army decided that they wanted a conventional
helicopter, and if they ever wanted speed, they would buy a tilt rotor.
Last I saw, the #2 S-69/XH-59A was covered in plastic, mothballed, out
back of the Sikorsky plant in Stratford. The #1 ship, which crashed
early in the program, was turned into a wind tunnel model and was at
NASA/Ames, last I knew.
Maury Markowitz
In <3509DE...@amiwest.com> David Lednicer wrote:
> The further out the flapping hinge is, the higher the head moment and
> the higher the control power.
Ok, I suppose that makes sense (although I don't completely grok it yet).
Rotary-wing isn't my area!
> mechanical flapping hinge further out than a couple of percent (the
> Brantly-Hynes helicopters being an exception to this).
What did they do?
> With a "rigid" rotor, such as on the Bo 105,
That looks a lot like a German name, is this a WWII aircraft you are
referring to?
> Yup, two J-60s urging it forward to up to 238 knots in level flight
Wow!
> Co-axials, like the Kamovs have mechanical hinges with low offset. To
> avoid rotor-rotor contact, they are well separated vertically. The ABC
> has very, very rigid blades that don't need excessive vertical
> separation.
With you so far.
> In high speed forward flight, the retreating blade stalls on a
> helicopter.
Right, ok.
> On the ABC this is no big deal and the two rotors cancel
> out each other's moments. On a co-axial, each rotor is trimmed to have
> no moment. Hence retreating blade stall is a limiting factor on top
> speed for a co-axial.
Ok, you lost me here. On the coax it's "trimmed out", do you mean the
pitch on the retreating side is set to minimize the effect, or does trim in
this case refer to something else. Either way, why is there a max speed in
which this works?
Ohhhhh, wait. Now I get it. On the ABS you just let the thing stall
because you don't care. On the coax you do have to care, so you have to trim
the blade out. So on the coax you either lose out because you have to trim
out moments and stall a blade, or you don't stall the blade and get leftover
moments.
Just how bad is a blade stall in a helo?
> True, but remember - Sikorsky initially pitched the ABC against the
> tilt rotor for JVX.
The whassahoozit?
> be a tilt rotor. Additionally, the ABC was pitched for LHX
This one I know, it got canned a couple of years back, right?
> Last I saw, the #2 S-69/XH-59A was covered in plastic, mothballed, out
> back of the Sikorsky plant in Stratford. The #1 ship, which crashed
> early in the program, was turned into a wind tunnel model and was at
> NASA/Ames, last I knew.
Let's hope it gets into a museum somewhere!
Maury
Gilbert Armbruster
Several folks have asked about oil injection.
The ROTAX-582 in the Mini-500 has a Mikuni oil injection pump. I'm told
this same or similiar pump is used by many outboard two-stroke engines
and is very reliable. The pump is between the Bing carbs and is driven
by the same gear shaft that turns the rotary intake valve. Therefore the
pump RPM is directly proportional to the engine RPM.
In a helicopter as BWB so aptly points out the engine turn 100%-104% all
the time except at idle on the ground. Therefore the oil pump turns at
100% to 104% RPM also.
It would at first seem that the amount of oil injected is therefore
constant like the RPM and does not vary with engine torque or power
output. THIS IS NOT SO.
There is a one to three splitter on the throttle mechanism. Two of the
cables go to the Bing Carbs and one goes to a valve on the oil pump
body. As you add throttle the oil pump valve opens and increases oil
flow into the intake manifold just downstream from the carbs and just
before the rotary intake valve.
Therefore the amount of oil injected is related to engine/oil-pump RPM
and to throttle position. I'm afraid that all I know on the subject if I
have a chance I will look through my manuals and see if I can find the
charts that indicate how much RPM, and how much throttle position
effects the oil flow.
Anyone? Please jump in and add more to this or correct any errors.
Gil Armbruster, Mini-500 Serial #76, 165 hours to-date
guar...@erols.com
David Lednicer wrote:
>
> Maury Markowitz wrote:
> > How so, because it was effectively doubled?
>
> rotor, such as on the Bo 105, you get rather high effective flapping
> hinges and high manouverability. We had a video at Sikorsky of a Bo 105
> doing a full aerobatic routine, including manouvers impossible to do in
> an airplane.
Heard this while I was in the Army: a newly-minted warrant officer is on
his first tour flying helos for the Army (thinks he's hot shit) and is
piloting a US Army UH-1H in West Germany. Alongside comes a civilian Bo
105, which slows down to take a look-see. They formate for a few
seconds and wave back and forth, then the Bo 105 does a full roll around
the Huey, after which it hauls for the horizon, leaving the Huey in its
exhaust fumes...
John Hairell (guar...@erols.com)
JIM105
>> With a "rigid" rotor, such as on the Bo 105,
>
>referring to?
The Messerschmitt BO-105 is a German design. They also get bent out of shape
if you say they have a "rigid" rotor. They call it a "hingeless" rotor. I
can't tell you what the difference is ( I am not convinced there is a
difference).
Of course now that MBB and Aerospatiale have merged into one big happy family
(hehe) all the machines are now officially known as Eurocopter. Of course
calling the BO-105 a Eurocopter is like calling the Hughes 500 the MD..excuse
me the Boeing....excuse me the Bell....oh just forget it.
Jim
Hiflyer07
>if you say they have a "rigid" rotor. They call it a "hingeless" rotor. I
>can't tell you what the difference is ( I am not convinced there is a
>difference).
The difference is that it is not "rigid"; the "hingless rotor" flaps about the
same as a "hinged" rotor: it just bends instead of having a flapping hinge, If
it were really made "rigid", the blades wouldn't bend and flap, and would
probably have to weigh many tons.
Bob T
Maury Markowitz
> We were told at the time that the reason for scrapping the AH-56 was
> that the cost of the black boxes and modules got out of hand. There was
> little problem with retreating blade stall since the rotor unloaded at
> speed due to the stub wings.
Cool. Did you just pitch it to zero?
> Question: Why did we pay more to cancel the Heavy Lift Helicopter (HLH)
> project than it would have cost to complete a flyable ship?
How heavy is heavy? Anything like that British 4-rotor monster?
Maury
Arnold Christensen
What British 4 rotor monster? Is this something of recent design? I
have not seen anything about it in recent press.
> How heavy is heavy? Anything like that British 4-rotor monster?
>
> Maury
--
Chris the Bigfoot, 65-66 B Co, 228th ASHBn(Hooks)(First Hooks in
Country), Panther 140, 1st CAV, 1st Team, 1st String, original
Boatperson (Boxer) and 71 Air Vietnam Chief Tech Insp, Arlington, TX,
ab...@airmail.net
Arnold Christensen
Badwater Bill
I find you post very interesting and informative. I only have a
couple of thoughts concerning the oil injection. You mention that
your EGT is okay at all power settings and that means your fuel/air
ratio's are looking good for the jetting needle profile. I agree.
What I'm not so sure about, however, is if the EGT and fuel flow has
much to do with the injection of the lubrication from that metering
port at the rotor valve. I think you could be seriously shy on oil
and have a good EGT because the fuel flow and air flow are okay.
What I'm trying to say is that the oil injection in the Rotax 582
could be shut off completely and your EGT would be fat dumb and happy
at about 1050 F or so. You wouldn't know it. I kind of like Ralph
from Oregon's idea of mixing about 1% oil in the fuel as a sort of
backup. Does Rotax recommend that or does Fetters?
So, I'm still a bit confused about how the oil injection is calibrated
and pre-flighted. It seems to me that it could get clogged and you'd
never know it since your fuel flow and air flow could be right on at
the altitude you operate. Altitude is another thing that worries me
about 2-strokes -and as you know, I own one myself. The jetting
needle is profiled for one altitude only. As you go up you're rich
and as you go down your lean for the fixed needle profile.
I love the idea of the power to weight ratio of a 2-cycle engine but
if you put them in a flying machine that has to operate at a bunch of
different altitudes, it seems to me that you're never tuned (except at
one specific altitude/pressure). All of this is a bit tricky in a
helicopter and the heli is tricky to begin with. I would have bought
a Mini-500 kit years ago if I didn't have these concerns. In fact I
sent for the info pack in 1992 before the first kit was available.
I've wanted one of these so bad for so long, my teeth hurt. I just
can't justify risking my life on that 2-stroke in this application.
I wish that DF would have let Rinke continue too. I'm in agreement
with all of you on that one. Competition is essential in driving R &
D. I don't think it's over yet. I think DF will have to back down on
that no-mod clause in that contract or his sales will plummet.
The turbine might not be the final answer to this either but it looks
better to me than the 2-stroke. It's too bad there isn't a good
reliable, cheap, mostly aluminum, 4-cycle out there that can put out
the same power without running the guts out of it, and maybe there is
one. I have great concerns about the Exec-162 also. The only way to
get power is to pump air and fuel. If you use a little engine and you
get a lot of horsepower out of it, you have to turn it fast. What do
they turn that one at? I thought it was something like 5500 rpm.
That's up in the scary zone for me too or I'd have bought one of them
a few years ago.
The Robie is really the only thing I see right now that is truly
reliable. They derate the O-320 to about 120 horsepower. I think the
rpm is about 2700 and it's a four-stroke. That combination is almost
bullet proof. I run the same engine in my RV-6 Experimental and pull
160 hp out of it. In that application the engine goes 2000 hours and
rarely fails.
But, the Robie costs an arm and a leg.
There just ain't no free lunch!
Badwater Bill
On Fri, 13 Mar 1998 23:40:10 -0500, Gilbert Armbruster
<garmbr...@erols.com> wrote:
>Several folks have asked about oil injection.
>
Gilbert Armbruster
BWB, I believe your right that the EGT's would not indicate that one or
both cylinders was not getting oil. I'm not sure if manufacturers went
to pumps because they had better control over the correct amount of oil
under varying conditions or because maybe folks could not be trusted to
add the correcy amount or any amount to the fuel. The Mini-500 uses a
meshed oil filter right at the oil tank to keep stuff out of the oil
pump and oil injectors. Every agrees that you should use a good
two-stroke oil and don't mix different brands. It would not be pretty if
mixing cause coagulation or something.
It's very convenient NOT to carry around two-stroke oil every where you
go. Just fill the oil tank and your good for about 7-8 hours of flight,
oil wise. I find that my altitude ranges from about 200msl to 2500msl
but mostly I fly at 1000MSL. This isn't much of a range and I find that
once I had run the engine about 50 hours, that I make only an occasional
seasonal change to the jetting.
I believe if you get it properly jetted so that your restricting fuel
flow with the proper jet for a given throttle position that the you can
pretty much keep the egt's constant in a hover, cruise, or descent. The
key is the right jets.
I see alot of Rotax's that are running on the needle jet all the time.
That is to say, the needle jet is too small, or the jet needle is too
large. In these cases the low power high RPM condition (a descent)runs
very hot and is very temperature sensitive. You can find this out by
changing the main jet to something larger and noticing that the hover or
high throttle setting EGT's do not change. This is because the needle
jet and the jet needle are to restictive. This is a dangerous condition
that I have found that several folks who had engine seazures had. They
need to get more fuel through the Needle, Needle jet combination and
restrict the full throttle position fuel flow with the main jet. In the
full or almost full throttle condition the needle jet, jet needle should
be less of a fuel flow restriction then the main jet. I run a much
larger needle jet then most Mini-500's I know, and run a smaller main
jet. The result I get are plenty of power on the top end without
superheating in a descent.
There are a lot of good articles around that explain how the BING carb
works. If your are going to fly a two-stroke helicopter the pilot needs
to understand understand the physics of the engine and carb.
The disclaimer: Every thing I said here could be wrong. Use your own
head and good judgement. Don't fly without good temperature gauges and
look at them often.
How about some other post from some folks with success or otherwise in
two-strokes?
Gil Armbruster Mini-500 serial #76, 165 hrs to date.
Hiflyer07
Seems to me one reasons for going to pumps is that such would presumably
provide a constant supply of oil regardless of the amount of fuel being burned.
In the helicopter the rpm is constant and, hence, the oil required is
constant--- while the amount of power produced, and fuel, hence, also oil,
varies from that for full power to just enough to turn the engine in a
near-power-off descent. I think the oil requirement would be constant
reagardless of power and fuel flow. Anyone have any thoughts????
Gilbert Armbruster
Since writing the material I posted earlier I had a chance to talk with
Eric Tucker about the ROTAX-582. Mr Tucker makes a living conducting
seminars on Rotax Engine maintenance and rebuilds the certified Rotax's.
He recently attended the Mini-500 builders seminar in DFW and spoke for
a little more then an hour on the ROTAX-582. This gentlemen has
inventigated the cause of un-told numbers of ROTAX engine failures and
his opinions are well recognized. We could have easily spent the entire
day with just him on the agenda.
I have asked Mr Tucker he would spend some time at Sun-n-Fun with the
Mini-500 owners and talk about how best to maintain and operate our
engines. I believe I will get him for a couple of hours to come down to
chopper town and talk with us. I will post details next month. He also
indicated if you have had a ROTAX engine problem bring your piston or
rod to Sun-n-Fun and he will be glad to look at it and give you his
thoughts based on his investigative experience.
I feel that my previous post which talked about the fact that the
throttle opens a valve on the oil pump may mislead people some what.
A large amount of the oil delivered by the pump is delivered as a
function of the engine RPM and the valve on the pump has a much smaller
effect on the amount of oil delivered then does the RPM.
I think this was the very reason ROTAX went to the pump. The amount of
oil required by the engine is more closely related to the RPM of the
engine then to the throttle position. So in a helicopter at 100% RPM no
load we are getting a large ratio of oil to gas and the engine is being
lubricated fine. When the throttle is opened further and the engine is
loaded some additional oil is also pumped in.
I'm was told that the most likely symptom of insufficient oil is a ROD
bearing failure not a seized piston. Most of the ROTAX-582's I've heard
of with problems have siezed or scuffed a piston.
I'm told that a seized piston is usually an indication of a combustion
heat expanded piston, dragging on a cool cylinder wall that has not
expanded to provide sufficient wall to piston clearance.
On my ship I ensure that the oil valve is beginning to open the minute
that the throttle starts to move. So I believe that I have good oil
flow.
The oil is injected just in front of the rotary intake valve and the
moment the valve opens the connecting rod needle bearings are right
there in front of the intake and get hit with the incoming oil. The oil
is then slung around the crankcase and lubricates the pison and
bearings.
Please consider this additional info and remember I don't do this for a
living. But I do fly a two-stoke helicopter. These are just my opinions
or recollections of conversations with persons whose opinions I respect.
PLEASE if you have some better info post it here on this subject. It is
a shame to damage a person or ship on account of an preventable engine
failure.
Several experience Mini-500 Pilot/Builders plan to be at Sun-n-Fun and
plan to put on some seminars if there is any interest shown. I will tell
you how to express your interest later in the month. I am looking for
someone with a Mini-500 that has their FAA flight test area restrictions
flown off (must be legal to fly at Sun-n-Fun) that might be interested
in having a couple of experience builders track and re-balance the
aircraft at Sun-n-Fun as part of a balancing seminar for other builders.
Prefer an aircraft that the builder thinks could be smoother or has some
cyclic stick shake. We will show how to use the Dynamic Solutions
balancer to track and balance the aircraft. Not sure what date we will
be doing it on yet.
Gil Armbruster.
JStricker
That's my experience as well in the outboard two-strokes.
Typically, piston breakage is cause by timing. Piston melting and seizing
is caused by improper mixture and/or inadequate cooling. Bottom end failure
is caused by inadequate/improper oiling. Doesn't take much to stop all
those little needles from rolling freely.
John Stricker
--
Remove the "nosp..........." Oh hell, you folks know what to do and
why I had to put it in. If one of you real humans wants to contact me:
"I didn't spend all these years getting to the top of the food chain
just to become a vegetarian"
Gilbert Armbruster wrote in message <350CB5...@erols.com>...
>I did a further post on this oil injection topic. The amount of oil in a
>ROTAX-582 that is oil injected I'm told is more a function of the RPM of
>the engine and oil pump then the valve on the oil pump that opens with
>throttle.
>
>That makes sense, some of the oil injected is based on the RPM and some
>of it based on the load. I also posted that lack of oil usually produces
>a rod or rod bearing failure not a piston seazure.
>
>Gilbert Armbruster.
Copterdktr
>Seems to me one reasons for going to pumps is that such would presumably
>provide a constant supply of oil regardless of the amount of fuel being
>burned.
>In the helicopter the rpm is constant and, hence, the oil required is
>constant--- while the amount of power produced, and fuel, hence, also oil,
>varies from that for full power to just enough to turn the engine in a
>near-power-off descent. I think the oil requirement would be constant
>reagardless of power and fuel flow. Anyone have any thoughts????
Using pumps would presumably increase the oil to fuel ratio during low power
(descending) operation. Wouldn't this possibly cause a problem with fuel
ignition? Maybe two-strokes for helos aren't such a good idea.
Maury Markowitz
In article
<845354A8E6A6A958.3D5A5218...@library-proxy.airnews.net>,
Arnold Christensen <ab...@airmail.net> wrote:
> What British 4 rotor monster? Is this something of recent design? I
> have not seen anything about it in recent press.
No, 50's. Looked like a bus with props. Actually it looked a lot like
that blimp with the four helos attached. They planned it for commuter
service in London.
Maury
Gilbert Armbruster
Hiflyer07 wrote:
>
> Seems to me one reasons for going to pumps is that such would presumably
> provide a constant supply of oil regardless of the amount of fuel being burned.
> In the helicopter the rpm is constant and, hence, the oil required is
> constant--- while the amount of power produced, and fuel, hence, also oil,
> varies from that for full power to just enough to turn the engine in a
> near-power-off descent. I think the oil requirement would be constant
> reagardless of power and fuel flow. Anyone have any thoughts????
WingDisk
Gil, we're talking to experts and amateurs- BUT WHERE IS ROTAX in all this? If
you search you can find a dead page at www.bombardier.com, or skidoo stuff. But
where is the "ask Dr. Goodrotax" page? Surely a multimilliondollar
multinational corporation who makes goodstuff like the Twin Otter (my uncle
flies 'em) could devote some REAL ENGINEERING EXPERTISE in our unwashed,
unsavory (speaking for myself) direction?
I'm Anonymous Cause I Irritate the Big Dogs,
Mini-500 Lover #421
Lorenzdav
>When you move this rotor disk through the air, the advancing blades
>produce more lift and the retreating blades product less; this tilts
>the cone toward the retreating side. If you put a _second_ rotor
>coaxial with the first, but rotating the other way, its retreating
>blades will be over the lower rotor's advancing blades -- the
>high-side blades of the bottom rotor bending up toward the low-side
>blades of the upper rotor.
as far as i know, if the retreating blade stalls, the reaction is 90 degrees
later, that meens, the disk tilts aft, the same happens for the
retreating blade of the other disk. Also a stalling blade has a much bigger
amount of drag, which is the main problem, why a retreating blade stall
in a normal helicopter can not be recovered
Stan Gosnell
lore...@aol.com (Lorenzdav) wrote:
>as far as i know, if the retreating blade stalls, the reaction is 90 degrees
>later, that meens, the disk tilts aft, the same happens for the
>retreating blade of the other disk.
The ship rolls left, with some pitch up.
> Also a stalling blade has a much bigger
>amount of drag, which is the main problem, why a retreating blade stall
>in a normal helicopter can not be recovered
It can be easily recovered. Just reduce pitch & airspeed. I have
done more than once. We used to practice it in the Army, long ago &
far away.
--
Regards,
Stan
Gary Allen
>....... Also a stalling blade has a much bigger
>amount of drag, which is the main problem, why a retreating blade stall
>in a normal helicopter can not be recovered
What??? Since when?
Gary
chu...@greatlakes.net
In article <19980316041...@ladder01.news.aol.com>,
wing...@aol.com (WingDisk) wrote:
>
>
> I'm Anonymous Cause I Irritate the Big Dogs,
> Mini-500 Lover #421
>
know,,,,,IF YOU CAN.......
-----== Posted via Deja News, The Leader in Internet Discussion ==-----
http://www.dejanews.com/ Now offering spam-free web-based newsreading
Lorenzdav
>>as far as i know, if the retreating blade stalls, the reaction is 90 degrees
>>later, that meens, the disk tilts aft, the same happens for the
>>retreating blade of the other disk.
>The ship rolls left, with some pitch up.
why does it roll left?
>> Also a stalling blade has a much bigger
>>amount of drag, which is the main problem, why a retreating blade stall
>>in a normal helicopter can not be recovered
>It can be easily recovered. Just reduce pitch & airspeed. I have
>done more than once. We used to practice it in the Army, long ago &
>far away.
ok, you are right, the retreating blade stall can be recovered, i thought of
a stall because of low rotor rpm, which can (as far as i know - at least in
an R22) not be recovered.?
regards
lorenz
David Lednicer
Maury Markowitz wrote:
> > mechanical flapping hinge further out than a couple of percent (the
> > Brantly-Hynes helicopters being an exception to this).
>
The Brantly-Hynes helicopters have flapping hinge about 30-40% of the
way out on the blade. I am not certain how they make this work, but
they do fly OK.
> > With a "rigid" rotor, such as on the Bo 105,
>
> That looks a lot like a German name, is this a WWII aircraft you are
> referring to?
The Bo 105 is the helicopter that MBB had in production in Germany from
1967 to recently. The Eurocopter EC 135 has superseded it in
production.
> Ohhhhh, wait. Now I get it. On the ABC you just let the thing stall
> because you don't care. On the coax you do have to care, so you have
> to trim the blade out. So on the coax you either lose out because you > have to trim out moments and stall a blade, or you don't stall the
> blade and get leftover moments.
You got it!
> Just how bad is a blade stall in a helo?
At speed over 200 mph, real bad.
> The whassahoozit?
JVX became the V-22 Osprey.
> This one I know, it got canned a couple of years back, right?
No, LHX became the RAH-66 Comanche.
David Lednicer
> Question: Why did we pay more to cancel the Heavy Lift Helicopter
> (HLH) project than it would have cost to complete a flyable ship?
Because Boeing Vertol never did have a transmission designed that could
handle the power and still not weigh too much. They were working on
advanced spiral gearing to fix this, but they never seemed to have
solved the problem completely. I think the answer instead was split
torque paths, which Mil used on the Mi-26 transmission, but knowledge of
this came too late.
Maury Markowitz
In <350E9F...@amiwest.com> David Lednicer wrote:
> > Just how bad is a blade stall in a helo?
>
> At speed over 200 mph, real bad.
Detructively? What exactly "is the problem" if a blade stalls? Sudden
drop of one side of the craft? A spin? Blade comes off? I only fly fixed
wing where a stall is "ok" - perhaps hard to recover from but it's not likely
to take your wings off. Is it basically the same issue on a helo, or is this
possibly deadly to the frame?
> JVX became the V-22 Osprey.
Gotcha.
> > This one I know, it got canned a couple of years back, right?
>
> No, LHX became the RAH-66 Comanche.
Didn't the -66 get killed? Or had it become the undead?
Maury
vic
> > Question: Why did we pay more to cancel the Heavy Lift Helicopter
> > (HLH) project than it would have cost to complete a flyable ship?
>
>
> Because Boeing Vertol never did have a transmission designed that could
> handle the power and still not weigh too much. They were working on
> advanced spiral gearing to fix this, but they never seemed to have
> solved the problem completely. I think the answer instead was split
> torque paths, which Mil used on the Mi-26 transmission, but knowledge of
> this came too late.
>
my question about the dollars? If there was a contract price for a
flyable demonstrator, and if Boeing Vertol could not deliver, why did
the government pay them off at an amount greater than the contract
price?
Agcatman
>Trouble is, it is hard to put a<BR>
>> mechanical flapping hinge further out than a couple of percent (the<BR>
>> Brantly-Hynes helicopters being an exception to this).
Does the hinge outboard on the blade of a Brantly flap? I thought it was just
a lead-lag hinge. But I don't really know.
Stephen Austin
Austin Ag Aviation
Comm. Rotorcraft/Helicopter, CFI and CFII Helicopter
Comm. SEL and MEL
Instrument Airplane and Helicopter
jlb...@ibm.net
Lead-lag only.
David Lednicer
Maury Markowitz wrote:
> What exactly "is the problem" if a blade stalls?
Blade stall causes some moments that must be trimmed out, but the worst
symptom is vibration, which can get pretty bad.
DWillis529
it flaps as well
Gary Knutson
And interestingly enough, a Brantly is one of the smoothest (low
vibration) ships that I have ever flown. It is a "strange" looking
design and I've never seen it used elsewhere.
DWillis529 wrote:
>
> it flaps as well
Ken Duffey
jlb...@ibm.net wrote:
snip.....
> The Kamov design bureau in Russia builds counterrotating rotor > helicopters with more than three blades per set.
The Kamov series of helicopters - Ka-25 Hormone, Ka-27/32 Helix, Ka-29
Helix, Ka-50 Hokum and Ka-52 Alligator all have three blades per set -
six blades in total.
I can't think of any Kamov co-axial design that has more than three
rotors per set ?????
Ken Duffey